Common sunflower [Helianthus annuus L.][HELAN] Photographs

Texas blueweed [Helianthus ciliaris DC.][HELCI][CDFA list: A] Photographs Map of Distribution



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[
SYNONYMS] [GENERAL DESCRIPTION] [SEEDLINGS] [MATURE PLANT] [ROOTS and UNDERGROUND STRUCTURES] [FLOWERS] [FRUITS and SEEDS] [HABITAT] [DISTRIBUTION] [PROPAGATION/PHENOLOGY] [MANAGEMENT FAVORING/DISCOURAGING SURVIVAL] [SIMILAR SPECIES] [CONTROL METHODS]

SYNONYMS:common sunflower: annual sunflower, wild sunflower, H. a. ssp. jaegeri (Heiser) Heiser, ssp. lenticularis (Douglas) Cockerell, H. a. var. macrocarpus (D.C.) Cockerell

GENERAL DESCRIPTION:

SEEDLINGS:common sunflower: Cotyledons oblong, 15-40 mm long, joined at the bases, smooth. First few true leaves opposite, dull green, covered with short bristly hairs that are rough to touch. Margins weakly round-toothed. Subsequent leaves alternate. No description available for Texas blueweed.

MATURE PLANT:Boths species have a strong pungent odor, especially when crushed.

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ROOTS and UNDERGROUND STRUCTURES:

FLOWERS:Showy composite flower heads solitary on long peduncles. Ray flowers yellow.

FRUITS and SEEDS:Similar to those of commercial sunflower. Pappus scales 2(4), deciduous.

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HABITAT:

DISTRIBUTION:

PROPAGATION/PHENOLOGY:

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Cultivation (to a depth of 20 cm at least every 2 months for Texas blueweed) reduces survival.

SIMILAR SPECIES:Unlike common sunflower, prairie sunflower [Helianthus petiolaris Nutt. ssp. petiolaris][HELPE], an introduced annual, has phyllaries typically less than 4 mm wide that are not conspicuously ciliate and truncate to wedge-shaped leaf bases. Disturbed sites in the San Francisco Bay region and Southern California, excluding deserts. To 450 m (1475 ft). Maximilian sunflower [Helianthus maximilianii Schrader][HELMA] is an introduced ornamental that has occasionally escaped cultivation. It has short rhizome-like roots. Unlike Texas blueweed, Maximilian sunflower lacks blue-green glaucous foliage and has alternate entire leaves 10-30 cm long, usually folded along the midribs, and without wavy margins. In addition, disk flower corolla lobes are yellow. Disturbed sites in southern San Joaquin Valley (Fresno Co.) To 100 m (330 ft).

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CONTROL METHODS:

Prevention: Texas blueweed is an aggressive perennial sunflower that is native to the grasslands of the south central United States. It naturally persists in low densities in native grasslands, but thrives in cultivated or heavily disturbed areas. Its reproductive strategy is primarily vegetative, from root buds on lateral roots. Seed studies from Texas have shown less than 1% of the total seed produced are viable. However, blueweed seed may have reached California in contaminated alfalfa or oats grown in Texas. Blueweed is highly competitive in several crops and cropping systems including cotton, wheat, and sorghum. Texas blueweed is a class A noxious weed in California. In agricultural fields, prevent new blueweed infestations by planting certified crop seed and cleaning equipment after working in infested fields.

Mechanical: The root system of Texas blueweed is composed of two distinct parts: an extensive network of shallow lateral roots with numerous root buds, and deeply penetrating feeder roots. New shoots arise from root buds on the laterals and form dense semi-circular patches. Hoeing, grubbing, or hand pulling small patches may be effective, if continually repeated for several years. Intensive cultivation repeated throughout the growing season for at least two years has been effective in eradicating blueweed. This requires plowing to a minimum depth of seven inches at monthly or bimonthly intervals. Infrequent cultivation will likely spread the weed, as rootstocks may be severed and dragged by tillage equipment. Tillage implements should be thoroughly cleaned after working in infested areas, to prevent spread of root pieces to new fields.
There is no information available regarding mowing as a control strategy. Mowing plants may prevent seed production, but should not be done after seed set.

Grazing: Livestock may graze young, newly emerged shoots, but tend to avoid plants as they mature. Maintaining a healthy, competitive range may prevent blueweed from becoming established. However, it will persist in native grasslands and may increase if overgrazing occurs.

Chemical: Certain herbicides have provided control of blueweed in the south central United States. However, repeated applications may be necessary, and control may vary depending upon the year. Dicamba, 2,4-D, MCPA, and picloram have been reported to control blueweed. Clopyralid, which is now labeled for use in California rangelands, is very effective on common sunflowers and may also control or suppress blueweed. Imazapyr and glyphosate may also be effective for blueweed control. Refer to the herbicide label for rates and timings.

References
Keeling, J. W. and Abernathy, J. R. 1988. Woollyleaf bursage (Ambrosia grayi) and Texas blueweed (Helianthus ciliaris) control by dicamba. Weed Technology 2:12-15.
Roche, C. 1991. Texas blueweed (Helianthus ciliaris D.C.). Pacific Northwest Extension Publication 364
Schoenhals, M. G. and Wiese, A. F. 1988. Control of blueweed and silverleaf nightshade. Proc.South.Weed Sci.Soc. 41:89

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